Ruby里4种比较函数（equal?, eql?, ==, ===）详解
Ruby里面有4种比较方法，equal"htmlcode">
a = "abc" #=> "abc" b = a + "" #=> "abc" ?> a == b #=> true a.object_id #=> 70255156346640 b.object_id #=> 70255156340640
=== - 用在 case 语句里时会调用的方法
通常用在 case 比较调用该方法，比如
case some_object
when /a regex/
# The regex matches
when String
# some_object is kind of String
when 2..4
# some_object is in the range 2..4
when lambda {|x| some_crazy_custom_predicate }
# the lambda returned true
end
等同于
if /a regex/ === some_object
# The regex matches
elsif String === some_object
# some_object is kind of object
elsif (2..4) === some_object
# some_object is in the range 2..4
elsif lambda {|x| some_crazy_custom_predicate } === some_object
# the lambda returned true
end
eql"htmlcode">
所以什么时候应该覆盖这个方法就看你想让他在 Hash 比较时如何表现。 equal"htmlcode">
记忆方法
1 == 1.0 #=> true
1.eql"htmlcode">
[1] pry(main)> hash = Hash.new
#=> {}
[2] pry(main)> hash[2] = "a"
#=> "a"
[3] pry(main)> hash[2.0] = "b"
#=> "b"
[4] pry(main)> hash[2]
#=> "a"
[5] pry(main)> hash[2.0]
#=> "b"
[6] pry(main)> hash[2.00] = "c"
#=> "c"
[7] pry(main)> hash[2.0]
#=> "c"
q = User.first
User Load (40.4ms) SELECT "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT 1
#=> #<User id: 1, email: "ryan@wongyouth.com">
q2 = User.first
User Load (0.4ms) SELECT "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT 1
#=> #<User id: 1, email: "ryan@wongyouth.com">
q.equal? q2
#=> false
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